Fuel injection apparatuses for operating an internal combustion engine have been generally known for many years. With a so-called common rail injection system the fuel is fed into the respective combustion chamber of the internal combustion engine by injectors, in particular by piezo injectors. In this process the quality of combustion is dependent on the pressure of a high-pressure accumulator connected upstream of the injectors. To achieve the highest possible specific performance of the internal combustion engine with low pollutant emissions, the pressure of this high-pressure accumulator must be regulated. It is thus possible to achieve injection pressures of 1600 to 1800 bar for the fuel using a high-pressure pump and a pressure accumulator.
Pressure regulation of the high-pressure accumulator can be achieved in different ways. Depending on the embodiment of the injection system it can be done with a pressure regulation valve in the high-pressure region and a volume regulation valve on the low-pressure side of the high-pressure pump or just by means of a volume regulation valve on the low-pressure side of the high-pressure pump. Only the second instance, in other words pressure regulation based on a volume regulation valve, is examined below. The high-pressure accumulator pressure is regulated here by regulating the volume flow in the low-pressure region of the high-pressure pump. This volume flow regulation is dependent both on the system requirement, which is determined by the quantity of fuel injected into the combustion chamber, and the quantity of fuel exiting from the injectors due to switching leakage losses.
During volume flow regulation it must be taken into account that after a regulation intervention the high-pressure pump must be filled with fuel before fuel can once again be pumped into the high-pressure accumulator, thus bringing about a pressure rise in the high-pressure accumulator. The time period required to fill the high-pressure pump up with fuel restricts regulation speed for stability reasons.